Adjustable length heat tunnel for varying shot lengths

ABSTRACT

An improved heat tunnel is provided for use with a thermo-forming press. The heat tunnel includes a first oven body having a heat source therein for applying heat to a web of thermo-formable material as the web is supported therein. The tunnel includes a second oven body having a heat source therein for applying heat to a web of thermo-formable material as the web is supported therein. Furthermore, the tunnel has an adjustable length tunnel body carried between the first and second oven bodies and configurable to adjust the overall length of the heat tunnel so as to realize a desired delivery of heat to a web of material being passed there through.

TECHNICAL FIELD

This invention relates to apparatus for heating a web of plasticmaterial prior to processing in a thermal forming machine when producingthin walled plastic articles.

BACKGROUND OF THE INVENTION

During the manufacture and forming of products from sheets or webs ofplastic material, ovens are used to preheat the web of material prior tomolding the plastic material into groups of plastic thin-walledarticles. Typically, the oven forms part of a thermo-forming machinehaving a thermo-forming press. A number of different articles can beformed from a sheet or web of plastic material as it is fed from astorage roll. Accordingly, a thermo-forming press produces a largequantity of molded articles by intermittently passing a progressingsuccession of adjacent sections, or shot lengths of web into the press,after which the web is stamped or formed. The mold is also used to holdor clamp the web in a stationary location while it is being stamped.Hence, the web is fed into the thermo-forming press in an intermittentfashion, and in footprints defined by the size and shape of the mold(top and bottom die) of the press as it operates in cycles on the web.

A typical prior oven construction consists of an elongate oven havingopen leading and trailing ends. Heating elements inside the oven, forexample resistance heaters, operate to heat successive portions of asheet as it is intermittently delivered into the thermal forming pressat a desired molding temperature. However, the ability to properly heata continuous thermo-formable plastic sheet or web of material to adesired temperature depends upon the amount of energy transferred to thesheet, which is, in part, dependent upon the amount of time that the webpasses through the oven. Typical oven constructions utilize an oven bodyhaving a finite length. Therefore, in order to tailor heat delivery to athermo-formable plastic sheet prior to feeding the sheet into athermo-forming press requires an adjustment of the stationary time thatthe wet, sits within the press and oven.

One problem encountered when attempting to adjust the heat delivery to athermal forming sheet passing through a finite length oven is thenecessity of tailoring the oven length to the particular application, oradjusting the stop time during which the thermo-forming press has lockedthe web in a stationary position. In normal operations, it is desirableto increase production rate. Therefore, it is desirable to operate athermo-forming press in as short a cycle time as is physically possibleby the constraints of the press operation and web deformation betweenpairs of interlocking dies. Therefore, it is desirable to tailor heatdelivery to the web through some other means. One possibility is tocontrollably adjust the heat output from each of the thermal resistanceelements carried within art oven. However, such an attempt at heatdelivery requires careful monitoring of heat being delivered and timeduring activation for each of the elements. Hence, a complex controlscheme is needed to track and target heat and delivery values for eachof the elements in an oven.

Therefore, a need has arisen to provide for a simple and economical ovenconstruction that enables the adjustable tailoring of heat delivery to aweb of thermo-formable plastic sheet material to be passed through athermo-forming press that operates on a staged or intermittent stampingprinciple.

The objective of the present invention is to provide an improved heattunnel construction for varying shot lengths and heat delivery to a webof material that can always be tailored to relate to the differentregions of the product being formed from the web.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a schematic side view representation of an adjustable lengthheat tunnel and thermo-forming press which together form athermo-forming machine in accordance with the preferred embodiment ofthe invention;

FIG. 2 is a plan view of the thermo-forming machine, including theadjustable length heat tunnel according to the machine of FIG. 1;

FIG. 3 is a temperature profile of a web of thermo-formable plasticsheet material plastic material as it progresses through each of fourfoot-print successive stages leading to stamping within the press asillustrated in FIG. 2;

FIG. 4 is a side view of a preferred construction of the adjustablelength heat tunnel depicted schematically in FIGS. 1-3;

FIG. 5 is a plan view of the adjustable length heat tunnel of FIG. 4;and

FIG. 6 is a vertical sectional view taken along line 6--6 of FIG. 5illustrating the construction and heating element arrangement within theadjustable length heat tunnel of FIGS. 4-5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws "to promote the progressof science and useful arts" (Article 1, Section 8).

In accordance with one aspect of this invention, an improved heat tunnelis provided for use with a thermo-forming press. The heat tunnelincludes a first oven body having a heat source therein for applyingheat to a web of thermo-formable material as the web is supportedtherein. The tunnel includes a second oven body having a heat sourcetherein for applying heat to a web of thermo-formable material as theweb is supported therein. Furthermore, the tunnel has an adjustablelength tunnel body carried between the first and second oven bodies andconfigurable to adjust the overall length of the heat tunnel so as torealize a desired delivery of heat to a web of material being passedtherethrough.

In accordance with another aspect of this invention, an improved heattunnel includes a first oven body constructed and arranged to apply heatto a web of thermo-formable material. The heat tunnel also includes asecond oven body constructed and arranged to apply heat to a web ofthermo-formable material. Furthermore, the heat tunnel includes anadjustable length tunnel body carried between the first and second ovenbodies and configurable to adjust the overall length of the heat tunnelso as to realize a desired delivery of heat to a web of material beingpassed through the heat tunnel.

A preferred embodiment of a thermo-forming machine is generallydesignated with the reference numeral 10. Machine 10 includes anadjustable length heat tunnel, or oven 12 as illustrated in FIG. 1. Aweb 14 of thermo-formable plastic material is passed through the tunnel12 and into a thermo-forming press 16. Tunnel 12 is constructed to havean adjustable length, enabling production and delivery of a desiredamount of heat energy to a web 14 of thermo-formable plastic material asit is being delivered through the tunnel 12 and into a thermo-formingpress 16. A plurality of thin-walled articles 18 are produced from theweb by pairs of mating male and female die assemblies 20. Each dieassembly is formed from a pair of mating male and female die that arecarried by an upper platen 22 and a lower platen 24, respectively. Upperplaten 22 is lowered into contact with a clamping grid 26 to lock inposition the web, after which the lower platen 24 is raised during themolding of articles 18. Typically, lower platen 24 includes a supportmember having a plurality of male die members that are raised from thelower platen, causing the web to be drawn into cavities within the upperplaten 22.

According to FIG. 1, web 14 is delivered in an intermittent and meteredmanner from a storage roll 28 through tunnel 12 and press 14 byactivating one or more servo drives. Typically, the web 14 is supportedby a plurality of rollers. At least one pair of the rollers, matedtogether on opposite sides of web 14, are driven by a servo drive,causing the web 14 to be fed upon activation of the servo drive.Activation of the pair of rollers delivers the web through tunnel 12 andpress 16 onto a waste storage roll 30. In one system, articles 18 aresimultaneously severed from web 14 after formation in press 16. Inanother version, articles 18 must be removed from web 14 after they arethermo-formed by implementing a secondary cutting operation. In thelatter case, the remaining scrap web is wound onto storage web 30 forsubsequent reprocessing.

According to FIG. 1, heat tunnel 12 is formed from a leading oven member32, a trailing oven member 34 and a telescoping and medially positionedtunnel assembly 36. Telescoping tunnel assembly 36 is supported andsealed at either end to members 32 and 34, respectively. One or moreheat sources are provided within members 32 and 34. Tunnel assembly 36does not have a heat source, enabling a compact and telescopicconstruction. However, heat supplied from members 32 and 34 provides asufficient supply of heat within assembly 36 so that heat delivery toweb 14 is reasonably uniform. Alternatively, it is possible to provideheating elements within assembly 36, pursuant to the heat sourcesdisclosed below for use with members 32 and 34.

Leading oven member 32 of FIG. 1 is formed from an oven body 38 and anentry hood 40. Similarly, trailing oven member 34 is formed from an ovenbody 42 and an exit hood 44. Oven bodies 38 and 42 are formed from aplurality of structural frame members that are enclosed with a layer ofexterior sheet metal. Similarly, hoods 40 and 42 are each formed from afolded sheet metal construction. Additionally, entry hood 40 and exithood 42 each have a reduced-size mouth portion 46 which reduces heatloss from heat tunnel 12 at each end.

According to the construction of FIG. 1, leading oven member 32 andtrailing oven member 34 are carried by a support frame (not shown) inrelative movable relation along the axis of web 14. In this manner, therelative positions of members 32 and 34 can be adjusted, causing tunnelassembly 36 to telescope therebetween. Hence, assembly 36 can belengthened or shortened. In this manner, the total length of the region48 where heat is applied to web 14 can be adjusted to realize a desiredheating of a shot length 50 of web that is to be formed in press 16.Preferably, shot length 50 is defined by the length of the foot print ofpress 16, and web 14 is advanced the same length as the shot lengthbetween successive forming cycles.

FIG. 2 illustrates a plan-view schematic representation of heat tunnel12 adjusted to an exemplary desired length for a web 14 ofthermo-plastic material being passed therethrough. Web 14 is moved instages to advance the web 14 to the next position only when press 16 isopen. Hence, web 14 remains stationary in five successive shot-lengthpositions prior to being advanced into a sixth-stage press operation.Stages 1 through 5 are illustrated by reference letters A-E,respectively. The length of tunnel 12 has been adjusted to produce areasonably uniform application of heat to web 14, imparting uniformmolding characteristics across an advanced shot-length of the web whileit is being molded. Hence, a higher quality of molded articles are moreconsistently produced during a molding operation. All of this isaccomplished without adjusting or varying the application of heat withinthe tunnel. Further tailoring of heat delivery can be carried out byadjusting the heat delivery within the tunnel, as will be discussedbelow.

FIG. 3 illustrates a temperature profile for differential heat as it isapplied to web 14 by heat tunnel 12 at each of stages A through E. Forthis case, it is assumed that heat has been applied uniformly from theheating elements within the tunnel. FIG. 3 also illustrates the totalamount of applied heat that has been delivered to web 14 during stages Athrough E. The cumulative heat delivered at stages A-E produces a shotlength of web at stage F having a fairly uniform temperature profile.Hence, the shot length of web at stage F is formed in press 16 while ithas desired uniform temperature characteristics.

According to FIG. 2, leading edge 52 of tunnel 12 has been adjustablypositioned to a desired length by extending or telescoping tunnelassembly 36. A multiple number of successive shot-lengths are held instationary locations A-E within the tunnel 12 during each operatingcycle for press 16. Leading edge 52 has been positioned withapproximately four inches of overlap past the leading edge of station B,and into station A.

For example, as shown in FIG. 2, shot-length station "A" is the firstposition of web 12 where heat is applied for a series of stamping cyclesleading to stamping by press 16 at station "E". Only the right edge ofweb 14 is heated while at station A, due to overlap of edge 52 and heatloss from the end of tunnel 12. Shot-length station "B" represents theposition of web 12 during the next press operation. Shot-length station"C" represents the third illustrated shot-length cycle, or the thirdcomplete stationary press cycle in which web 14 is heated by tunnel 12.Shot-length station "D" represents the fourth press cycle position ofweb 14 prior to being stamped by press 16. Similarly, shot-length "E" isthe fifth and final press cycle position of web 14 being heated prior tobeing formed.

It is readily apparent from viewing FIG. 2 that tunnel 12 is placed asclose as possible to press 16 to minimize heat loss prior to forming.Typically, the space between the trailing end of tunnel 12 and theleading end of press 16 is no more than. Alternatively, the distance canbe greater or less. Web 14 extends outside of the trailing edge 54 ontunnel 12 a slight amount, just before being advanced to shot-lengthstation "F" where it is stamped. Therefore, heat application duringshot-length "E" is not uniform as heat escapes from the trailing edge oftunnel 12. Similarly, as web 14 is positioned at station "A", heatescapes from leading edge 52, causing localized heating of web 14 priorto entry into tunnel 12.

The above staged heating of web 14 is illustrated according to thetemperature profile depicted in FIG. 3. Following the shot-length stagesA-E, a non-uniform amount of heat is applied to web 14 while in thestage "A" position, prior to entering tunnel 12. Prior to entering stage"A", the edge of web 14 adjacent to tunnel 12 is locally heatedaccording to the shaded region 56. The differential heat which isapplied to web 14 while it is positioned in station "B" appears to benearly uniform, in light of the even nature of heating provided by theconstruction of tunnel 12 (and particularly oven body 32) therein.Similarly, web 14 is uniformly heated while located at stations "C" and"D". However, a slight drop occurs within tunnel assembly 36 since thereare no heating elements within that portion of the tunnel. The finalstation "E", which precedes movement into station "F" where a stampingoperation is performed, shows an uneven heating distribution, as heatescapes from the trailing edge 54 of oven 12 (as depicted in FIG. 2).The heat lost from the tunnel trailing edge is denoted generally by thearea of region 58.

Finally, region "F" has been plotted to illustrate the total, orcumulative heat applied to web 14 from regions A-E, and shaded region56. Web 14 progresses through and out of tunnel 12, acquiring heat alongthe way, preceding the final cycle operation where web 14 is stamped bypress 16 at station "F". Hence, the heat which has built up in web 14within a defined "shot-length" (i.e. the length of press 16) as it movesthrough tunnel 12 is illustrated by the total applied heat as plotted atstation "F".

For purposes of visualizing the uniform application of heat to a"shot-length" of web 14 during a stamping operation at station "F", theaddition of areas within the region bounded by curve 60 produces an areaof reasonably uniform applied heat for presentation at station "F".Additionally, or alternatively, arrays of switchable heating elementscan be provided within members 32 and 34, at either end of tunnel 12,enabling even further tailoring of heat application of a web 14 beingpassed through tunnel 12. Additionally, other suitable lengths fortunnel 12 can be realized by merely adjusting the overall length. Forexample, if the "shot-length" of web 14 is changed due to a change ofdie size being used in press 16, an operator merely needs to adjust thelength of tunnel 12 to a desired length to achieve a suitabletemperature profile of the web passing through the oven. Furthermore, ifless heat is needed for a given operation, the oven can be shortened toreduce the number of stations that the web will sit within the ovenprior to being stamped.

FIG. 4 illustrates an elevational view of one construction for heattunnel or oven 12. According to this construction, oven bodies 38 and 42are each constructed by securing sheet metal via a plurality of rivetsor fasteners to a metal framework. A pair of guide rollers 62 aremounted on each side of body 38 and 40, respectively. For example, aroller bearing guide roller can be used to form roller 62. Preferably,roller 62 on bodies 38 and 42 are positioned along a common horizontalaxis. Alignment of rollers 62 enables the mounting of heat tunnel 12along a pair of inwardly facing and opposed c-channel guide tracks alongwhich each of roller 62 are received. In this manner, the c-channeltracks form raceways there along in which the rollers 62 track. Onesuitable track construction is depicted and described below withreference to FIG. 6. Hence, oven members 32 and 34, as well as tunnelassembly 36 are supported by rollers 62 on a framework supported track.

Additionally, overhead frame assemblies 64 and 66 are configured atop ofbodies 38 and 42, respectively, for enabling rapid opening of portionsof bodies 38 and 42 to expel heat. During certain operations, it may benecessary to quickly remove heat from the oven. Each assembly 64 and 66is formed from a pair of vertically extending support members, mountedinwardly of the sides of tunnel 12, and extending upwardly therefrom.

According to FIG. 4, telescoping tunnel assembly 36 is formed from aplurality of telescoping hood members 68-71. In this case, member 71telescopes within an adjacent end of member 70, member 70 telescopeswithin an adjacent end of member 69, and member 69 telescopes within anadjacent end of member 68. Preferably, roller bearings facilitatesliding contact there between. Alternatively, low-friction slidingcontact points can be used. Preferably, a terminal lip flange preventsadjacent members from pulling completely apart. Member 68 is rigidlyaffixed and supported to body 38 along a common adjoining edge.Preferably, member 68 is secured to body 38 with a plurality offasteners. Similarly, member 71 is rigidly affixed and supported to body42 along a common adjoining edge.

According to the construction depicted in FIGS. 4 and 5, hoods 40 and 44have top and bottom surfaces that taper, forming a slot-shaped mouthopening through which the web is passed. Additionally, the top andbottom faces have a curved, or tunnel shaped construction suitable formaintaining a desired volume within the hood.

According to FIG. 5, the layout of rollers 62 on either side of members32 and 34 is visibly apparent. Two pair of rollers are used to supporteach member. Furthermore, the two pair of rollers are positioned on eachmember spaced apart as far as practical along each member, to impartstability to the m ember as it is rolled along a guide rail.

A portion of oven body 38 on member 32 is shown with the sheet metalskin removed in FIG. 5. An array of structural framework members 72which support the sheet metal skin, rollers 62, hood 40, telescopingmember 68, and frame assembly 64 are visible. Members 72 are preferablysecured together with threaded fasteners, rivets, or welds. Thesurrounding sheet metal skin is then secured to the outside of theframework with fasteners.

Also visible in the partial breakaway view of FIG. 5 is an array ofresistive heating elements 74 which are supported in nested adjacentrelation within oven body 38. Each element 74 is supported at oppositeends from a pair of top frame members or bottom frame members (asdepicted in FIG. 6, below). In operation, electricity is supplied to oneor more of the elements, causing them to produce heat along their entirelength.

A further feature of this invention is provided by the use of an arrayof elements 74, configured transversely across the path of a web. It ispossible to only turn on elements 74 that lie directly over portions ofa shot-length that are to be formed in a press. For example, a press mayonly be used to form a web along a middle one-third section, requiringheat only in this area. Therefore, elements 74 that lie over thatportion of a web within a station, and as part of a shot-length, onlyneed be turned on. In this manner, heat delivery can be tailored so thatit relates to the different regions of the web where the product is tobe formed, even as the web is passed in stages through a tunnel.

FIG. 6 illustrates a vertical cross-sectional view of oven body 38,taken along line 6--6 of FIG. 5. A pair of top and bottom heatingelements 74 can be seen clearly in this view. Each element isconstructed and arranged to form a curved surface along a portion thatlies across a web being passed within the oven body. The bottom element74 is shown in sectional view, depicting the heating wire carried withinits metal outer body. Element 74 has nearly all of its heat delivery atthe right corner, since the internal heating wire is coiled along theright corner. The coil produces the bulk of the heat output from theelement. The top element 74 is identically constructed. However, thenext row of elements are heated on the left corner. This patternalternates with each successive row of top and bottom elements.

In this manner, a suitably even distribution of heat is applied across aweb contained therein, both along the top and bottom sides. Bydelivering heat to the corners, in alternating left and right arrays, amore uniform temperature distribution is realized within tunnel 12. Thisis due largely to the fact that tunnels or ovens tend to collect heat attheir centers. Furthermore, the sheet metal sides 84 of the oven bodytend to dissipate heat. Therefore, more heat is required along the edgesand any attempt to supply heat along the outer edges serves to mitigatethis problem. Additionally, elements 74 are configured further away fromweb 14 along the central region.

To support an array of heating elements 74 within oven body 38, a pairof longitudinally extending frame members 76 are formed in the top andbottom regions of body 38. One end of each element 74 is mounted to asheet metal pan which is formed between each pair of frame members,providing a structural support member therebetween. Electrical wiring(not shown) is then fed through members 76 from a single common source,or feedline.

Web 14 is shown in FIG. 6 being carried between the top and bottomelements 74 by a pair of water-cooled chain driven rail guides. A chainhaving a plurality of teeth perforates and engages web 14 on eitheredge, engaging the web to move it through the tunnel. Water coolingprevents overheating of the web where it contacts the chain and railguides.

FIG. 6 also illustrates the support rail structure that supports andguides members 32 and 34 (of FIGS. 1-5). A pair of rollers 62 are shownin seated engagement with a complimentary pair of guide rails 82. Eachrail 82 is removably mounted on top of a longitudinally extendingtubular steel support rail 78 by a support plate 80. Roller 62 isentrapped between plate 80 and guide rail 82, upon being assembledtogether. Plate 80 and rail 82 form a c-channel shaped member, whenaffixed together. Furthermore, plate 80 is then secured to rail 78 witha plurality of threaded fasteners. Rails 78 are supported by framemembers that mount to the press at one end, and mount to a verticalsupport frame (not shown) at an opposite end. In this manner, plate 80forms a longitudinal raceway on top of which each of rollers 62 seat inrolling engagement.

To support the loads of tunnel 12, rollers 62 are attached to ovenbodies 38 and 42 by individual roller carrier support assemblies 86.Assemblies 86 are formed from metal brackets which affix to the sides ofeach oven body, for example, to body 38 of FIG. 6. Various alternativemounting techniques can be used to support oven bodies 38 and 42 inrelative axially movable relation, enabling telescoping of tunnelassembly 36 therebetween (as depicted in FIG. 5).

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

We claim:
 1. A heat tunnel for use with a thermo-forming press,comprising:an entrance oven body having an entrance opening configuredto receive a web of thermo-formable material, and a heat source thereinconfigured to apply heat to the web as the web is transportedtherethrough; an exit oven body having an exit opening substantiallylevel with the entrance opening and configured to receive the web, and aheat source therein configured to apply heat to the web as the web istransported therethrough; and an adjustable length tunnel body carriedbetween the entrance and exit oven bodies and configured to jointogether the entrance oven body and the exit oven body in adjustablyspaced apart relation and operative to adjust the overall length of theheat tunnel so as to realize a desired delivery of heat to a web ofmaterial being conveyed in an intermittent and metered mannertherethrough.
 2. The heat tunnel of claim 1 wherein the heat sourcecomprises a resistive heating element.
 3. The heat tunnel of claim 2wherein the heating element comprises a crescent-shaped wire formconstruction.
 4. The heat tunnel of claim 1 wherein the heat sourcecomprises an upper and a lower array of resistive heating elementscarried within the oven body, the web being passed there between toimpart heating there along.
 5. The heat tunnel of claim 1 wherein thetunnel body comprises a plurality of telescoping tunnel members, one ofan adjacent pair of members slidably received within another of theadjacent pair of members.
 6. The heat tunnel of claim 1 furthercomprising a hood mated with an end of the oven body opposite the tunnelbody.
 7. The heat tunnel of claim 1 wherein one of the oven bodiesfurther comprises a plurality of rollers carried thereon, and the heattunnel further comprises at least one support rail having a raceway forreceiving the rollers movably there along, the one oven body movablewith respect to the other oven body, imparting extension/retraction tothe adjustable length tunnel body carried therebetween.
 8. The heattunnel of claim 7 wherein the other of the oven bodies further comprisesa plurality of rollers carried thereon, the at least one support railhaving a raceway for receiving the rollers movably there along, the oneoven body movable with respect to the other oven body, impartingextension/retraction to the adjustable length tunnel body carriedtherebetween.
 9. The heat tunnel of claim 1 wherein a pair of supportrails are provided, one on either side of the oven body, constructed andarranged to receive rollers therein for movably carrying the oven bodythere along.
 10. The heat tunnel of claim 1 wherein the heat source ofthe entrance and the exit oven bodies each comprise a plurality oflaterally disposed and elongate heating elements constructed andarranged to be independently operable so as to enable tailored deliveryof heat to the web of material that relates to the product being formed.11. A heat tunnel, comprising:a first oven body constructed and arrangedto apply heat to a web of thermo-formable material; a second oven bodysupported in similar elevational relationship with the first oven body,the second oven body constructed and arranged to apply heat to a web ofthermo-formable material; and an adjustable length tunnel body carriedbetween the first and second oven bodies and configurable to adjust theoverall length of the heat tunnel so as to realize a desired delivery ofheat to a web of material being conveyed through the heat tunnel. 12.The heat tunnel of claim 11 wherein at least one of the oven bodiescomprises a resistive heating element constructed and arranged to heatthe web of material being supported therein.
 13. The heat tunnel ofclaim 12 wherein the at least one oven body comprises an upper and alower array of resistive heating elements carried within the oven body,the web being passed there between to impart heating there along. 14.The heat tunnel of claim 11 further comprising a hood mated with an endof the oven body opposite the tunnel body.
 15. The heat tunnel of claim11 wherein the tunnel body comprises a plurality of telescoping tunnelmembers, one of an adjacent pair of members slidably received withinanother of the adjacent pair of members.
 16. The heat tunnel of claim 11wherein one of the oven bodies further comprises a plurality of rollerscarried thereon, and the heat tunnel further comprises at least onesupport rail having a raceway for receiving the rollers movably therealong, the oven body movable with respect to the other oven body,imparting extension/retraction to the adjustable length tunnel bodycarried therebetween.
 17. A thermo-formable web heat tunnel,comprising:a first oven body having a heat source comprising an upperand a lower array of resistive heating elements configured to apply heatto a web of thermo-formable material as the web is conveyed therebetweento impart heating there along; a second oven body having a heat sourcecomprising an upper and a lower array of resistive heating elementsconfigured to apply heat to a web, of thermo-formable material as theweb is conveyed therebetween to impart heating there along; and anadjustable length tunnel body carried between the first and second ovenbodies in associated relation and configurable to adjust the overalllength of the heat tunnel so as to realize a desired delivery of heat toa web of material being intermittently conveyed therethrough.
 18. Theheat tunnel of claim 17 wherein the tunnel body comprises a plurality oftelescoping tunnel members, one of an adjacent pair of members slidablyreceived within another of the adjacent pair of members.
 19. The heattunnel of claim 17 wherein each heat source comprises an array ofheating elements configured transversely across a travel path of a webreceived there along.
 20. The heat tunnel of claim 19 wherein the arrayof heating elements is configured to be selectively enabled viaapplication of electricity so as to produce heat directly over a desiredshot-length of a web which is to be formed in a thermo-forming presspositioned immediately downstream thereof.